While heavy duty bumper systems have been built which are capable of meeting the above noted collision impact requirements, they have normally been relatively complicated of design and therefore costly to manufacture as well as being heavier than is to be desired.
The following patents are illustrative of bumper systems which have been designed to perform in environments similar to that of the subject invention:
U.S. Pat. No. 3,897,095 "Resilient Bumper Assembly"--Glance et al PA1 U.S. Pat. No. 3,902,748 "Pneumatic Energy Absorbing Bumper System For Motor Vehicles"--Bank et al PA1 U.S. Pat. No. 3,989,292 "Semi-Pneumatic Energy Absorbing Bumper System For Motor Vehicles"--Bank et al PA1 U.S. Pat. No. 4,103,951 "Semi-Pneumatic Energy Absorbing Bumper System For Motor Vehicles"--Bank et al
While not done in the manner of applicant, it is also previously known to have constructed a bus type bumper system utiliting a resilient foam material encased in elastomeric outer cover member.